KUFA, Iraq — A suicide car bomber struck amid a crowd of laborers across from a major Shiite shrine in southern Iraq on Tuesday, killing at least 53 people and wounding 105, officials and witnesses said as the United Nations reported that nearly 6,000 civilians were killed in Iraq in May and June alone.

In this town 100 miles south of Baghdad, the suicide attacker drove a minivan to a site where Shiite laborers gather to look for employment. He offered work, loaded the minivan with those who accepted and then detonated the vehicle, Najaf Gov. Asaad Abu Kalal told a Shiite television station.

The blast occurred about 7:30 a.m. across the street from Kufa’s gold-domed mosque, police Capt. Nafie Mohammed said. The shrine, located in a congested area of the city, marks the place where Imam Ali, cousin and son-in-law of the Prophet Muhammad, was mortally wounded.

Senior provincial health official Dr. Muthir al-Ithari said the casualty figure was from reports sent by hospitals in Kufa and nearby Najaf.

Prime Minister Nouri al-Maliki, a Shiite, condemned the attack and promised to track down and punish those who planned it.

Kufa is a stronghold of radical anti-American cleric Muqtada al-Sadr, whose movement controls the mosque. It appeared the blast was aimed at undermining al-Sadr’s position in Iraq’s sectarian struggle, much of which has been blamed on al-Sadr’s Mahdi Army militia.

Violence in Kufa followed Monday's attack in a market in Mahmoudiya, 75 miles north. Gunmen Monday killed at least 50 people, mostly Shiites, in an apparent attack on mourners at a funeral for one of al-Sadr’s militiamen.

Fears of civil war
Late Monday, police said they found 12 bodies in different parts of town — possible victims of reprisal killings.

Many Iraqis fear the retaliatory killings are the prelude to civil war. The campaign of intimidation and attacks is slowly transforming Baghdad into sectarian zones under the tacit control of armed groups that protect members of their sect.

The country’s largest Sunni Arab party called Tuesday for a conference of all religious and political leaders to end sectarian killing and save the country from sliding into civil war.

“There is a horrible escalation of violence and reaction to violence in Iraq,” the party said. “The Iraqi Islamic Party denounces the massacres that took place in Mahmoudiya and in Kufa and appeals to Iraqis to come to their senses instead of slipping into the abyss.”

The U.S. command said three American soldiers were killed in separate attacks on Monday — two in the Baghdad area and one in Anbar province west of the capital. At least 2,554 members of the U.S. military have died since the beginning of the Iraq war in March 2003, according to an Associated Press count.

Grim countsIn the first 17 days of July, at least 617 Iraqis have been killed in war-related violence, at least 527 civilians and 90 police and security forces, according to an AP count. An Associated Press count showed at least 450 Iraqis killed, including at least 306 civilians and 144 police and security forces, over the same period last year.

The AP count told only part of the grim tally. Nearly 6,000 civilians were slain across Iraq in May and June, a spike in deaths that coincided with rising sectarian attacks across the country, the United Nations said Tuesday.

The report from the U.N. Assistance Mission in Iraq describes a wave of lawlessness and crime, including assassinations, bombings, kidnappings, torture and intimidation.

Hundreds of teachers, judges, religious leaders and doctors have been targeted for death, and thousands of people have fled, the report said. Evidence suggests militants also have begun to target homosexuals, it said.

According to the report, 2,669 civilians were killed in May and 3,149 were killed in June. Those numbers combined two counts: from the Ministry of Health, which records deaths reported by hospitals; and the Medico-Legal Institute in Baghdad, which tallies the unidentified bodies it receives.

The report’s figures were higher than some other counts, but even the U.N. said many killings go unreported.

Doubts on U.S. role
The violence cast doubt on the U.S. strategy of handing over large areas of the country to Iraqi control, while keeping U.S. troops in reserve.

In Mahmoudiya, U.S. troops of the 101st Airborne Division reported hearing detonations and gunfire, the U.S. command said. But Iraqi troops are responsible for security there, and American soldiers do not intervene unless asked by the Iraqis.

Four soldiers and a former soldier from the division are accused of raping and murdering a teenage girl near Mahmoudiya on March 12. A sixth soldier is accused of failing to report the crime.

Al-Qaida leader arrested, another slain
National Security Adviser Mouwafak al-Rubaie said security forces had arrested the leaders of the Omar Brigade group, a wing of al-Qaida in Iraq that had claimed to have carried many deadly attacks throughout the country. He said the group was responsible for a July 1 bombing in Baghdad’s eastern Sadr City neighborhood that killed 66 people.

Al-Qaida in Iraq said last year it had formed the Omar Brigade to fight the Shiite militias. The group claimed to have killed many Shiite militia leaders since then.

Al-Rubaie also said an al-Qaida in Iraq member believed to have killed two captured U.S. soldiers last month had been fatally wounded in a clash with security forces.

Al-Rubaie told reporters that Diyar Ismail Mahmoud, known as Abu al-Afghani, was the killer of Pfc. Kristian Menchaca of Houston and Pfc. Thomas Tucker of Madras, Ore. The soldiers’ mutilated bodies were found after their capture in the area south of Baghdad known as the “Triangle of Death” for its frequent insurgent attacks.

Al-Rubaie did not say when Mahmoud was wounded or died.

In other violence, the bodies of five handcuffed men were found Tuesday dumped in western Baghdad and a roadside bomb struck a police patrol in Hawija, killing seven and wounding two.

Also Tuesday, a Polish military helicopter slammed into the ground at a base in central Iraq in an apparent accident just after takeoff, slightly injuring four crewmen and three journalists, an official said.